A grade 1 malignant tumour that closely resembles the tissue from which it originated is said to be what type?

A grade 1 malignant tumor that closely resembles the tissue from which it originated is classified as well-differentiated. This term indicates that the cancer cells maintain some characteristics of the normal tissue they derive from, which suggests a slower growth rate and a more benign behavior compared to less differentiated tumors. In well-differentiated tumors, the cells are organized similarly to healthy cells, and they often perform some of the functions of the original tissue, which typically leads to a better prognosis and more effective treatment options.

In contrast, terms like anaplastic, undifferentiated, and the dysplastic variation do not apply here since they refer to tumors with more aggressive behaviors, where the cancer cells lose the characteristics of the normal tissue. Anaplastic and undifferentiated tumors are poorly differentiated, meaning they have little resemblance to the tissue of origin and often exhibit rapid growth and invasion, while dysplastic changes refer more to pre-cancerous alterations rather than a classification of fully malignant tumors. Thus, a well-differentiated tumor remains the appropriate classification for this context.